Regulator-meter utilizing a beam of light for indication and regulation

ABSTRACT

REGULATOR-METER APPARATUS INCLUDES SIGNAL-RESPONSIVE METER MECHANISM FOR PROJECTING A LIGHT SPOT ONTO A TRANSPARENT SCREEN SUCH THAT THE SPOT TRANSVERSES THE SCREEN DURING SIGNAL-CAUSED MOVEMENT OF THE MECHANISM. THE POSITION OF THE SPOT ON THE SCREEN IS DETECTED BY TWO PHOTOSENSITIVE ELEMENTS WHICH DEFINE ONE SET POINT FOR THE REGULATOR PORTION OF THE APPARATUS, THE ELEMENTS BEING SPACED APART A DISTANCE SLIGHTLY GREATER THAN THE CORRESPONDING CROSSSECTIONAL DIMENSIONS OF THE SPOT AND HAVING THE OUTPUTS THEREOF CONNECTED TO DIFFERENT ONES OF THE SET AND RESET INPUTS OF A BISTABLE MULTIVIBRATOR. THE BISTABLE ASSUMES EITHER ITS SET OR RESET STATE DEPENDING UPON THE POSITION OF THE SPOT RELATIVE TO THE ELEMENTS. CIRCUITRY IS PROVIDED FOR EFFECTING INITIAL FULL-SCALE ENERGIZATION AND DE-ENERGIZATION OF THE MECHANISM, CAUSING THE BISTABLE TO ASSUME   A KNOWN INITIAL STATE, FOR EXAMPLE, THE RESET STATE. THE CROSS-SECTIONAL SHAPE OF THE SPOT IS DEFINED BY A SUITABLY APERATURED MASK, MOUNTED SO AS TO BE RESPONSIVE TO THE DISPLACEMENTS OF BOTH A PROPORTIONAL-EFFECT AND AN INTEGRAL-EFFECT BIMETALLIC ELEMENT.

Filed July: 14 1969 Sept. 20,197] -r EI'AL 1 r I 3,6065151 IREGULATOR-METER UTILIZING A BEAM OF LIGHT FOR INDICATION AND REGULATION2 Sheets-Sheet 1 M ATTORNEY Sept. 20, 1971 M, D ETAL 3,606,151

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United States Patent Oflice 3,606,151 Patented Sept. 20, 1971 Int. Cl.GllSd 23/22 U.S. Cl. 236-69 8 Claims ABSTRACT OF THE DISCLOSURERegulator-meter apparatus includes signal-responsive meter mechanism forprojecting a light spot onto a transparent screen such that the spottraverses the screen during signal-caused movement of the mechanism. Theposition of the spot on the screen is detected by two photosensitiveelements which define one set point for the regulator portion of theapparatus, the elements being spaced apart a distance slightly greaterthan the corresponding crosssectional dimensions of the spot and havingthe outputs thereof connected to different ones of the set and resetinputs of a bistable multivibrator. The bistable assumes either its setor reset state depending upon the position of the spot relative to theelements. Circuitry is provided for effecting initial full-scaleenergization and de-energization of the mechanism, causing the bistableto assume a known initial state, for example, the reset state. Thecross-sectional shape of the spot is defined by a suitably aperturedmask, mounted so as to be responsive to the displacements of both aproportional-effect and an integral-effect bimetallic element.

This invention relates to control apparatus and more particularly to aregulator-meter for measuring and controlling the temperature ofindustrial equipment, such as an oven.

Regulator-meters for controlling industrial equipment typically measurea parameter such as temperature, pressure or flow and maintain thisparameter in the vicinity of some predetermined value or set point.These regulators are often used to control ovens and the like in whichthe temperature must be held substantially constant and equal to somepredetermined value.

The meter portion of the regulator-meter generally includes agalvanometer to which is applied a voltage proportional to the parameterto be measured. The moving coil of the galvanometer drives a pointer,which typically mounts a flag or mask at the free end thereof; the maskmoving along a front scale bearing suitable indicia upon rotation of thepointer. A detecting system gives a yesor-no signal according to whetherthe position of the flag is to the left or to the right of the setpoint. This signal actuates a relay which may be considered as part ofthe regulator portion of the regulator-meter by reason of its moredirect interface with the means by regulating an associated apparatus(an oven, for example). Various conventional types of systems, which maybe photoelectric, capacitative or indicative in nature are currentlyused to detect the position of the flag. French Pat. No. 1,330,- 847, isexemplary of a system which is basically indicative in nature in that itemploys a metallic flag movable between two oscillating coils placed atthe set point to change the LC time constant and hence the frequency ofcoil oscillation. A change in coil frequency is detected to provide anindication of the position of the flag.

However, disadvantageously these pointer systems are relatively fragileand since the pointers rotate about a central axis, usually requirearcuate front scales. Furthermore, the pointer and the flag have arelatively high inertia which reduces the speed of response of thegalvanometer.

Projected-light type meters, on the other hand, do not have suchdisadvantages. Instead of employing mechanical pointers, projected lightmeters commonly use a light spot, that is, a concentrated beam of light,reflected from a mirror mounted to rotate with the moving coil of thegalvanometer. Unfortunately, the use of a light spot for regulationpurposes gives rise to numerous problems. One such problem is thatalthough it is a relatively simple matter to detect the passage of thespot at the set point, for example, by means of a photoelectric celllocated at the set point, it is a far more difficult proposition todetermine if this light spot is to the right or to the left of the setpoint after movement.

Further, for the meter to be wholly reliable, it is also necessary toprovide numerous safety measures. For example, should there be a failureof the lamp filament, momentary failure of the power supply or breakageof the sensor associated with the controlled equipment, the regulatormust react so as not to give erroneous commands which might damage theequipment. These problems, which did not occur with a moving vane, havenot been satisfactorily solved for meters employing moving light spots.

An object of the invention is to provide a regulatormeter without thedisadvantages mentioned hereinabove, using a light spot both forindication and regulation.

Another object of the invention is to provide a regulatormeter includinga simple light spot detection system which allows one to know at anytime, if the light spot is to the right or to the left of a set point.

A still further object of the invention is to provide a regulator-meterutilizing a movable light spot rather than a movable pointer, with allthe safety features needed for reliable operation.

According to the instant invention, a regulator-meter includes a mirrorgalvanometer for projecting a light spot onto a transparent screen, thelight spot traversing the screen along a defined path upon rotation ofthe mirror. The position of the light spot is detected by twophotoelectric elements which are located along the path of the spot. Twosuch elements define one of the regulator set points. The outputs ofthese two cells are respectively connected to the set and reset inputsof a bistable device. The bistable takes either one or the other of twocorresponding stable states when the light spot is resting on one sideor the other of the cell photosensitive element. A sweeping orfull-scale electrical signal is applied to and then removed from thegalvanometer when the unit is switched on initially in order to triggerthe bistable so that it always assumes the same initial state, forexample, the reset state.

:It is also known in the prior art to transform an operatingregulator-meter, which may be described as a yes-no or go-no-go type,into a proportional effect regulator by using a modulating bimetallicelement heated simultaneously by an intervening component, such as amotor, heating resistor or pump. The oscillations of the regulatedparameter around its set point are then considerably reduced. Inpractice, the proportional effect bimetallic element moves the set pointso that the regulator oscillates about an average frequency whichdetermines the proportional regulation range. Such a control for atemperature-regulated oven is especially typical.

In the proportional regulation range, heating of the oven and of thebimetallic element is established during intervals, the duration andfrequency of which depend upon the amount and speed of deflection of thebimetallic element and on the heating and cooling speeds of the oven.Generally speaking, the extreme points of the sweeping range of thebimetallic element are designed to be symmetrical relative to the setpoint. Fast heating ovens stabilize at a temperature very close to theupper limit of the regulation range and hence the effective heating timeintervals are very short, at least compared to the oven-cooling timeconstant. Slow heating ovens, on the contrary, stabilize at atemperature close to the lower limit of the proportional regulationrange, the effective heating time intervals being interrupted only for ashort time. Between these two extreme cases, all intermediate cases are,of course, possible.

To cancel the permanent systematic error due to proportional effectregulators, it is known to add an integral correction system. Anintegral correction bimetallic element may be used, the heating andcooling time constants of this second bimetallic element being generallycomparable to those of the oven and, in any case, long compared to theconstants of the proportional effect bimetallic element. Such systemsare described, for example, in French Pat. 1,222,293 and 1,223,299. Theeffects of proportional and integral effect bimetallic elements areopposed and inasmuch as the integral action bimetallic elementintegrates the successive heating intervals given by the modulationbimetallic element, the sweeping range of the modulation bimetallicelement is offset by a value proportional to the average energy appliedto the oven so that the true and set temperatures are driven toward, andfinally to, equality.

In the apparatus described in the patents mentioned hereinabove, theproportional and integral effect bimetallic elements vary the positionof the set point. However, this design is physically implemented byrelatively complex and fragile mechanical systems which it would bedesirable to simplify.

Therefore, a still further object of the invention is to provide anuncomplicated assembly of proportional and integral effect bimetallicelements which utilize to advantage a light spot and photoelectricdetecting cells.

According to this aspect of the invention, the light spot comprises areading spot and a regulating spot. The reading spot is obtained by anaperture extending therethrough configured to shape incident light intoa reading spot of desired cross-section, the mask being attached to themeter movement. The regulating spot is obtained by a regulation maskmounted on the end of a proportional effect bimetallic element. Theproportional effect element is associated with an integral effectbimetallic element syn chronously heated with said proportion effectelement, the deflections of said elements being opposed to each otherand the integral effect element having a long thermal time constantcompared to the proportional effect element.

As a result of the instant arrangement of integral and proportionaleffect elements, the manufacture of light spot indicator-regulatorspossessing both effects is made particularly easy. The cells whichdetermine the set points, after their initial positioning, need not besubsequently adjusted and the relatively complex and fragile mechanismwhich, up to now, has been used both for adjusting and causingoscillations at the set point is considerably simplified by separatingthe functionsand using an adjusting mechanism for the cells and anoscillating mechanism for the regulation mask.

The characteristics and advantages of the invention will be furtherenhanced by the description to follow which is given solely as anon-limitative example with reference to the attached drawings on which:

FIG. 1 is a perspective view of a regulator-meter according to theinvention showing the inner layout of the various components; and

FIG. 2 is a diagram of the electrical circuits used in the meter shownin FIG. 1.

Referring to FIG. 1, a regulator-meter comprises a housing of overallrectangular shape having a sidewallsZ and a rectangular cover 4 mountedthereon. The housing front wall 6 mounts a flat translucent screen 8 inscribed with scale indicia 10 and the housing rear wall 12 mounts aincandescent lamp 14. A condensing lens 16 is mounted in front of thelamp 1-4 to focus visible bimetallic element 27 of overall rectangularshape and having a midlength section surrounded by a heating resistor27. Bimetallic element 26 is attached to a spacer 28 which mounts a heatinsulated plate 29 composed of asbestos, for example, and a small metalblock 30 formed with a central bore in which is placed a heatingresistor 31, the resistor 31 being electrically insulated from the block30 by encapsulating in a material of relatively low heat conductivity,for example, ceramic. The block 30 is fixedly mounted to a secondbimetallic element 32, similar to the element 26, and attached to thesidewall 2. The assemblies of bimetallic elements 26 and 32 are suchthat they deviate in opposite directions when heated. The timesnecessary for the bimetallic elements to be completely deflected underthe effect of their respective heating resistors 27 and 31 are, forexample, approximately one and five minutes respectively. Adjacent to,and in optical alignment with, the aperture 22 is a dualcolortransparent filter 33, having, for example, a red filter section 34 anda green filter section 36 joined together in endwise relationship. Thefilter 33 is attached fixedly to a metal plate 38 which can pivotbetween two positions around a pivot pin 40 in directions perpendicularto the palne of filter 33. The position of the plate 38 is controlled bya solenoid 42. v

The light originating from bulb 14, after having passed through lens 16,slots 22 and 24 and filter 33 strikes a planar, reflective mirror 44inclined to incident rays of light 52 so as to reflect such lightthrough a further condensing lens 46. Light rays 54 leaving the lens 46are directed onto a mirror 48 mounted on the moving coil of agalvanometer 50 and form a colliminated beam or light spot 58 on thefront wall 6 of housing 2. The focal distance of lens 46 is selected soas to provide a clear image of the luminous object formed by aperture 24and triangular aperture 22. It will be noticed that the image isinverted relative to the luminous object, the triangular part 60 orindicating spot striking the translucent screen 8, and the elongatedpart 6, or regulating spot, impinging upon an opaque region beneath thisscreen, that is, on the opaque part of front surface 6. Galvanometer50is conventional with a moving coil 64 and magnetic parts 66. A carriage70 may be moved along a slideway 68 parallel to front surface 6 andlocated immediately behind this surface, this carriage 70 having twophotoelectric cells 72 and 74 mounted thereon. These two cells have theshape of two narrow, vertically oriented rectangles spaced apart adistance slightly less than the width of the regulation spot 62. Avertical axis located centrally or midway between these two cellsrepresents the position of the set point for regulation, this axis beingmaterialized by a pointer (not shown) attached to carriage 70' andlocated in front of translucent screen 8.

FIG. 2 shows the various electrical circuits of the indicator regulatorshown in FIG. 1, used for example, for measuring and controlling thetemperature of an electrical oven heated by a resistor 82. Thetemperature of the oven is sensed by a thermocouple 84 connected to theregulator-meter. Other temperature sensors such as resistor sensors maybe used in lieu of the thermocouple 84.

The regulator-meter is supplied with AC. current applied to atransformer 86 with three outputs. The first output is applied to thelamp 14. A resistor 88- connected in series with lamp 14 has itsterminals connected to a bias circuit 90. The second output oftransformer 86 is connected through a switch 92 to the heating resistors27 and 31 connected in series. The coil of electromagnet 42 is connectedin parallel to these two heating resistors 27 and 31. The third outputof transformer 86 is connected to a direct current power supply 93 theoutput of which is connected to a bistable flip-flop 94 through a switchshown in the form of a transistor 96. The base of transistor 96 isconnected to the output of bias circuit 90. Bistable 94 includes setterminal S connected to the photoelectric cell 72 and also referred toas C1, and a reset terminal R connected to the photoelectric cell 74also referred to as C2. A third cell 98 referred to as C3, is

also connected to the terminal R, the three cells being supplied withDC. voltage from supply +V. The output signal from bistable 94 isapplied to the coil 112 of an electromagnetic relay controlling a firstset of contacts 114 connected in series with the oven heating circuit 82and a second set of contacts 92, connected as described hereabove.

A relay 114 is controlled directly by the bistable 94. It is thuspossible to interpose, between this bistable and the coil of relay 112,a control circuit of the type described in applicants French patentapplication 141,329, filed Feb. 27, 1968 and entitled An ElectromagneticRelay Control System.

The thermocouple 84 is connected for sensitivity adjustment throughresistor 100 to the terminals of the galvanometer 50, a resistor 102representing the lead resistances. The galvanometer 50 is also connectedby means of a sweeping pulse circuit 104 to DC. voltage delivered bysupply 93, this voltage being taken off the collector of transistor 96.The sweeping pulse circuit 104 includes a differentiating circuit formedby capacitor 106 and a resistor 108 followed by a buffer-amplifier 110.The purpose of circuit 104 is to deliver to the galvanometer 50 asweeping pulse every time the supply 93 is switched on. The reasons forgenerating this sweeping pulse are explained in greater detailhereafter.

The DC. voltage produced by the supply 93 is also supplied by means oftwo conductors 118 and 120 to the input terminals of thermocouple 84.Conductor 118 incorporates a resistor 116 of high resistance value. Thecircuit formed by conductors 118 and 120 and resistor 116 cooperateswith the photoelectric cell 98 to stop heating of the oven in case thethermocouple 84 is broken, as will be explained subsequently.

In operation, thermocouple 84 generates a voltage which is a function ofthe temperature of the oven 80 and the deviation of the galvanometerspot is proportional to this temperature. It will, firstly, be assumedthat the oven is being heated and that its temperature is lower than theestablished set point. Luminous spot 58 is therefore to one side of thecells C1 and C2. Bistable 94 is in the active state and, therefore,closes switch 114. As the temperature of the oven increases the spot 58moves toward the right (assuming the observator looks at the frontscreen 8). When the regulation spot 62 encounters cell C1 connected tothe set terminal of bistable 94, nothing happens since this bistable isalready in the active state. On the other hand, when spot 62 encounterscell C2, bistable 94 returns to the passive or reset state and relay 114opens, thereby stopping the heating of the oven. Conversely, when thetemperature of the oven decreases, spot 62 returns towards the left andby traversing the cell C1 triggers bistable 94 into the active state,thereby closing switch 114. When the balanced temperature of the oven isobtained, the spot lies between the two cells C1 and C2. Since thespacing between the cells is very slightly less than the width of thespot the latter are permanently sensitized and a slight movement towardsthe right stops the heating and a slight movement towards the leftrestarts this heating. The set point is, therefore, properly maintainedon the central axis of the two cells C1 and C2.

In the foregoing explanation, it has been assumed, that the bistable 94was in the active state. In fact, this bistable is designed so that itsreset state is a privileged passive state characterized by a 0 bitpotential level on its logical 1 output terminal and its set state as anactive state characterized by a 1 bit level on its logical 1 outputterminal. In this manner, if a momentary open circuit or other failureoccures in the mains or other power supply failure occurs, when thetemperature of the oven is greater than the set value, the switches 92and 114 will remain open during the period the power supply isrestablished since the bistable will then return to the passive state.If the oven is cold when the indicator regulator is switched on, thebistable, therefore, remains in the passive state and the oven does notheat up. To avoid this disadvantage, the sweeping pulse circuit 104 isprovided. When the DC. voltage delivered by the power supply 93 risesfrom zero volts to its normal level, the differentiating circuit formedby capacitor 106 and resistor 108 produces a well-defined pulse which isapplied through buffer amplifier 110 to galva-nometer 50. In response tothis pulse, the spot 58 sweeps scale 10 up to maximum or full scaleposition and then returns to its normal operational position. Duringthis sweeping operation, regulating spot 62 energizes, successively,cells C1 and C2 and then in reverse order C2 and C1, if the temperatureof the oven is less than the said temperature. The bistable 94successively enters the active state when the spot passes over the cellC1 and to the passive state when the spot passes over the cell C2. Onreturn, nothing happens when the spot passes C1; the bistable 94returning to the active state when this spot passes over C1. This istherefore the desired heating position. This sweep happens in the samemanner when a momentary power failure occurs, thereby closing switch 114when the current is re-established if the temperature of the oven isless than the set point value.

Polarization circuit 90, resistor 88 and transistor 96 form a safetysystem in case of breakage of the filament of lamp 14. If this failureoccurs, the difference is potential between the terminals of resistor 88becomes null, circuit 90 no longer supplies the bias voltage to the baseof transistor 96 which thereupon stops conducting. Since coil 112 is nolonger supplied current, switch 114 opens and terminates the heating ofthe oven.

When the oven starts heating, the contact 92 of relay 112 closes andpower is applied to heating resistors 27 and 31 of the proportional andintegral effect bimetallic elements 26 and 32, respectively. Thedirection of deflection of the element 26 is such that mask 20, (whichis carried by said bimetallic element, is offset relative to the readingspot 60, which always indicates the true value of the temperature. Thedirection of deflection of the element 32 is opposite to that of theelement 26 so that the regulation range is constantly offset by a valveproportional to the average energy applied to the oven and that the trueand set temperatures are identical under stable operating conditions.

It can be seen that the mechanical assembly of elements 26 and 32 isparticularly simple, rugged and inexpensive. The same is true for thecells C1 and C2.

The switch 92 also controls solenoid 42 which controls the position ofthe two color filters 34 and 36 relatively to the opening 22. Duringheating of the oven, the solenoid pulls in so that the green filter 36is moved in front of the opening 22 and as a result a green reading spot'60 appears on the screen 8. Above the set value the solenoid pulls outand the filter 33 is pivoted until the red filter 34 moves in front ofthe opening 22 whereupon the reading spot 60 becomes red. This systemmakes it possible for the operator to ascertain, at a glance if and howthe system is operating.

Conductors '118 and 120, resistor 116 and the third photoelectric cell98 combine to form a safety device in case of breakage of thethermocouple 84. Cell 98 is current power supply, therefore, is appliedto the terminals of the thermocouple through resistor 116. Ifthermocouple 84 is not broken, the additional voltage applied togalvanometer 50 !by conductors 118 and 120 is negligible because thevalue of resistor 116 is very high compared to the internal resistanceof thermocouple 84. The measurement, therefore, is not affected. On theother hand, if the thermocouple is defective, all the power supplyvoltage is applied to the 'galvanometer. Conductors 118 and 120 areconnected in such a manner that when this voltage is applied, the spot58 deviates towards the left. Regulation spot 62 impinges onphotoelectric cell C2 which places bistable 94 in the passive state,thereby cutting the heating of oven 80. This safety system operates forlow impedance sensors. If a sensor of the variable resistance type isused, this safety system can be deleted since breakage of the sensorwould result in unbalance in the measuring bridge which would give adivation of the spot towards the maximum reading of the scale, therebystopping the heating. In this case, the cell C2 can also be placedbeyond the scale number representing the maximum value of interest.

The regulator-meter although described as being used to control thetemperature of an oven, could, of course,

'be used to regulate other types of apparatus requiring a yes or no typeregulation.

What is claimed is:

1. Regulation-indication apparatus having a predetermined set pointcomprising, an elongated light-transmitting screen, mechanism fordirecting a first portion of a visible beam of light onto said screen,said mechanism being displaced by a signal parameter under measurementwhereupon said beam moves relative to said screen along a path, pluralphotoelectric devices located at a position along said path andproducing output electrical signals when activated by a second portionof said beam, said devices being spaced apart in a direction parallel tosaid path a distance slightly greater than the correspondingcross-sectional dimension of the activating second portion of said beamso as to define therebetween said set point for the apparatus, abistable device having two inputs coupled to different ones of saiddevices and changing state in response to said output signals, means fordriving said mechanism with asignal of predetermined magnitudesufficient to move the second beam portion past said devices at leastonce, whereby said bistable device is caused to assume a predeterminedstate before being made solely responsive to the signal parameter undermeasurement, and regulating means under the control of said bistabledevice.

2. Apparatus according to claim 1 which further comprises, a lightsource, optical means for collimating light from said source, and firstand secondelements located in an optical path between said optical meansand said mechanism, said first and second elements having at least oneaperture therein for shaping said collimated light into said first andsecond beam portions, respectively, and said second element beingmovable relative to said optical path, and temperature compensatingmeans coupled to said second of said elements for displacing said secondelement relative to said optical path.

3. Apparatus according to claim 2 wherein said temperature compensatingmeans comprises, a proportional effect bimetallic device having afreely'movable end, said second element being mounted on said movableend.

4. Apparatus according to claim 2 wherein said temperature compensatingmeans comprises proportional and integral effect bimetallic devicesmutually coupled together, one end of one of said bimetallic devicesbeing coupled to said second element.

5. Apparatus according to claim 1 which further comprises, at least twodifferent light filters selectively displaceable into the optical' pathof said first portion of said light beam, and means under the control ofsaid bistable device for selectively displacing said filters.

6. Apparatus according to claim 1 which further comprises, a source oflight for said mechanism, and means coupled to the light source and tosaid bistable device responsive to a failure of said light source fordriving said bistable to a predetermined state.

7. Apparatus according to claim 6 which further comprises, a thirdphotoelectric device located at a position along said path of saidsecond beam portion and at one end thereof, and logic circuitry coupledto said bistable device and to said means for driving said mechanism sothat said second beam portion activates said third photoelectric deviceupon failure of said plural photoelectric devices, and means forsignalling the activation of said third device. a

8. Apparatus according to claim 1 which further comprises, power supplymeans for energizing at least the regulation portion of said apparatusand switch means coupled to said power supply means for selectivelycoupling said power supply means to said apparatus, and wherein saidmeans for driving said mechanism is responsive to the switch meanscoupling said power supply means to said apparatus whereby said bistabledevice is driven into said predetermined state substantiallysimultaneously with the application of power to the apparatus.

References Cited UNITED STATES PATENTS 1,930,496 10/1933 Wilson, et a1.236-69 3,271,677. 9/1966 Peter, et a1. 317 127X WILLIAM E. WAYNER,Primary Examiner US. Cl. X.-R.

